Conventionally, a slide structure has been provided on a seat cushion of a vehicle seat to position, and thus fix the vehicle seat at a desired position in a longitudinal direction of the vehicle through the seat cushion.
Explaining about the slide structure, it comprises an upper rail fixed on the seat cushion and a lower rail fixed on a floor of the vehicle. Both of the rails are disposed to extend in the longitudinal direction. More specifically, the upper rail fits with the lower rail so as to be slidable in the longitudinal direction.
The upper rail has been conventionally disposed above the lower rail disposed on the floor of the vehicle. The present inventor improved such a conventional slide structure. As shown in FIG. 14, both of the upper and lower rails were arranged to be vertical. That means that a vertical cross-section of the rail structure generally comprising a movable outer rail 702 corresponding to the upper rail, a stationary inner rail 704 corresponding to the lower rail, and a retainer was shaped to be elongated in the vertical direction. This causes a section modulus to be effectively secured with respect to a bending moment about a neutral line extending in the widthwise direction of the vehicle in the vertical cross-section of the rail structure, as compared with that with a cross-section shaped to be elongated in the horizontal direction.
Accordingly, the weight of the slide structure can be decreased by limiting the increase of the thickness of the rail, for instance, while at the same time a necessary strength thereof can be effectively secured.
However, the present inventor found out that such a slide structure raises a new following technical problem.
More specifically, upon a collision of the vehicle, a fitting relationship between the movable outer rail 702 and the stationary inner rail 704 is removed due to an impact load, so that a sliding function associated with the rails is lost.
In particular, a belt load acts on a rear portion of the movable outer rail 702 through a buckle portion 706 upon the collision, for instance. In such a case, since the belt is arranged to extend inwardly, diagonally and forwardly from a lower end of the one of the sides of the seat back, to an upper end of the other of the sides thereof, as shown in an arrow in FIG. 14, components of the belt load in three directions, these are, the one in the widthwise direction of the vehicle, the one in the vertical direction thereof, and the one in the longitudinal direction thereof are inevitably generated.
Especially, the component in the widthwise direction acts inwardly in the widthwise direction. Since a rail structure of the slide structure has only a clearance of about a few millimeters relative to the side frame of the seat cushion due to a limited space within the vehicle, the movable outer rail 702 extending in the longitudinal direction is caused to deform toward the one of the outer surfaces of the pair of the side frames S of the seat cushion C disposed inside of the movable outer rail 702 due to the component of the belt load in the widthwise direction.
This causes a load oriented outwardly in the widthwise direction, that is, opposite to the component of the belt load in the widthwise direction, to be exerted on the front portion of the movable outer rail 702 with a position of the movable outer rail 702 where it contacts the one of the outer surfaces of the pair of the side frames S being a fulcrum.
In such a case, since the movable outer rail 702 is disposed outside of the stationary inner rail 704, which is supported, and thus fixed by a leg 708 from inside, in the widthwise direction, a fitting relationship between the movable outer rail 702 and the stationary inner rail 704 is created with an opening portion of the C-shaped cross-section of the movable outer rail 702 being oriented inwardly in the widthwise direction, while an opening portion of the C-shaped cross-section of the stationary inner rail 704 being oriented outwardly in the widthwise direction. As shown in an arrow in FIG. 15, due to the load oriented outwardly in the widthwise direction, a force acts on the movable outer rail 702 so as to move its opening portion of the C-shaped cross-section away from the stationary inner rail 704, while another force as a reaction force to said force acts on the stationary inner rail 704 so as to move its opening portion of the C-shaped cross-section away from the movable outer rail 702, and thus, the fitting relationship between said two rails is removed.
Accordingly, a phenomenon in which a sliding function associated with said two rails is lost due to a belt load upon the collision can be caused. A relief of an injured passenger due to the collision can become too late because of such a phenomenon.